1. Field
The present disclosure relates to networking and particularly to peer-to-peer (P2P) traffic processing technologies and network address translator (NAT) traversal methods. In particular, the disclosed NAT traversal methods relate to establishing direct connections to clients behind symmetrical NATs and asymmetrical NATs.
2. Related Art
One currently used Internet protocol, IPv4, was originally designed to use a 32-bit address field (IP address) to identify a host. A 32-bit IP address is insufficient to assign a global (or public) IP address to each device on the Internet today.
To overcome this limitation, it was proposed (circa 1994) to assign public IP addresses not only to end-point devices but also to some designated network transition routers which isolate the end-points from the Internet, thereby dividing the network domain into a public domain and a number of isolated private domains. These so called “border routers” started performing a new and important networking task: translating (mapping) IP addresses between the private and the public domains, thus allowing a host within a local network to be able to communicate 2-way globally even though it has a local (private) IP address only. Border routers also hid their local network visibility from the outside, which turned out to be quite helpful for the security and protection of the isolated local networks. Due to this property, Border Routers also became firewalls.
Border Routers, along with a corresponding technique for IP address mapping and with associated security features, came to be referred to as Network Address Translators (NATs). In the meanwhile NATs became widely used both for security and for alleviating the IPv4 address shortage problem. IPv6 is a protocol designed to address the IPv4 address shortage problem. However, no matter the protocols involved, the computing world may still continue to deploy NATs in order to isolate private enterprise and home networks from external visibility.
Currently, there is widespread deployment of different NATs, i.e., NATs with different properties and modes of operation. NATs are not required to be compatible with each other such as in the way that NATs generate their IP address translations. NATs are manufactured by different OEMs, and not only differ from vendor to vendor but even from model to model. The history of NATs has generated an unpleasant side effect, which has become a serious issue and obstacle for many Internet applications: NATs break the end-to-end connectivity of devices and applications by often not allowing the establishment of peer-to-peer (P2P) communications. Almost all NATs block and reject the data transmitted directly between end-points from different private networks. Many contemporary P2P applications—voice over IP (VoIP), multimedia over IP, including Streaming Live A/V or Real-Time Interactive A/V, videoconference instant messaging, online gaming and even online gambling, et al.—seriously suffer from the presence of NATs as unwanted check points on the communication path. The presence of NATs is a limiting factor in the development of P2P applications especially in mobile wireless networks.
These and other disadvantages are overcome with the teachings described in the present disclosure.